In today's "information age" everyone wants their telecommunication systems, telephones, computers, audio-visual, and networks to work faster. Computer users expect their computers to be faster, programs to run faster, etc. Internet users expect files to download faster. Network users expect their files to transfer faster. As the technology advances so does the expectation for faster systems. People no longer want to wait for technology, everyone wants their information immediately. Further efforts are underway to provide fiber optic cables to homes (known as fiber to the home or FTTH).
Systems are becoming faster because the systems are able to handle higher data throughput rates. One of the reasons that data throughput rates are increasing is because the systems are able to handle larger bandwidths. However, greater and greater numbers of such systems are coming online in homes and offices. This in turn increases the demand for even more bandwidth. The present invention increases the bandwidth for fiber-optic systems. More particularly, the present invention increases the amount of beam splitting, combining, and wavelength division multiplexing in a fiber optic system using a light-pipe.
Present fiber-optic systems, which are improvements over coaxial-cable systems, have been constantly challenged by the demand of higher connectivity and higher data throughput rates (bit rates). The higher connectivity requires splitters and combiners that are able to split and combine a large number of light beams. The higher bit rates are able to take full advantage of the large bandwidths offered by optic fibers. Wavelength Division Multiplexing (WDM) is yet another technique to exploit optical fiber's large bandwidth capacity by combining signals based upon differing wavelengths into a single fiber.
Fiber-optic splitters split the signal from one fiber to n output fibers. Some of the popular present day splitters are fused fiber splitters (also called fused tapered splitters), planar waveguide splitters and cube beam splitters. Gradient Index (GRIN) lens splitters can be used as well, but they are not commercially available. Each of these splitters has their own strength and weakness. Fused fiber splitters are the most popular splitters to provide a 1-to-n split. The weakness of fused fiber splitters is their wavelength and polarization dependence. Planar waveguide splitters have a similar performance as fused splitters, but produce a more uniform and stable output among the fibers. There is a tendency to replace fused fiber splitters with planar waveguide splitters. Cube beam splitters are not used in fiber-optic networks by themselves. Typically a cube beamsplitter is used with a GRIN lens to collimate the beam from the tip of the fiber. When the beam passes the cube beamsplitter, the beam splits into two beams. Two GRIN lenses are then used to focus the two beams into two output fibers. Compared with fused fiber splitters, cube beam splitters are larger and more expensive.
Combining a number of signals at the same wavelength is an important way to perform time-division multiplexing. This is a weak area in fiber-optic networks. Neither fused fiber splitters, planar waveguide splitters, nor cube splitters are bidirectional devices. When they are used as combiners, the insertion loss is large. Dense wavelength division multiplexing (DWDM) is a very efficient method to utilize the large bandwidth offered by optical fibers. DWDM combines N signals at N different wavelengths into a single fiber. Present day DWDMs are based on two techniques: (1) grating (including regular grating, fiber Bragg grating, and arrayed waveguide grating), and (2) narrow bandpass filter. These two techniques have successfully increased the bandwidth of existing fiber networks. However, these techniques are very expensive. Other weaknesses are that the wavelengths of the signals must be precise. Any wavelength shift will introduce large insertion loss. Changing wavelengths of signals is not a trivial task. The wavelengths are not flexible. After the system has been built, it is difficult to add new wavelengths to expand the system's capacity.
A need therefore exists for DWDMs that can be used in optic fiber networks to maximize the bandwidth that the optical fibers can handle, and to be flexible enough for adding more signal channels in the future. A need also exists for splitters and combiners used in fiber-optic networks to provide high connectivity for single and multi-mode fibers with true wavelength and polarization independence. There is a further need for these devices to be capable of being mass produced in large quantities and to be affordable for a variety of communication situations.